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<div class="subTitle">org.apache.commons.math3.stat.correlation</div>
<h2 title="Class Covariance" class="title">Class Covariance</h2>
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<li>org.apache.commons.math3.stat.correlation.Covariance</li>
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<dl>
<dt>Direct Known Subclasses:</dt>
<dd><a href="../../../../../../org/apache/commons/math3/stat/correlation/StorelessCovariance.html" title="class in org.apache.commons.math3.stat.correlation">StorelessCovariance</a></dd>
</dl>
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<pre>public class <span class="strong">Covariance</span>
extends <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true" title="class or interface in java.lang">Object</a></pre>
<div class="block">Computes covariances for pairs of arrays or columns of a matrix.

 <p>The constructors that take <code>RealMatrix</code> or
 <code>double[][]</code> arguments generate covariance matrices.  The
 columns of the input matrices are assumed to represent variable values.</p>

 <p>The constructor argument <code>biasCorrected</code> determines whether or
 not computed covariances are bias-corrected.</p>

 <p>Unbiased covariances are given by the formula</p>
 <code>cov(X, Y) = &Sigma;[(x<sub>i</sub> - E(X))(y<sub>i</sub> - E(Y))] / (n - 1)</code>
 where <code>E(X)</code> is the mean of <code>X</code> and <code>E(Y)</code>
 is the mean of the <code>Y</code> values.

 <p>Non-bias-corrected estimates use <code>n</code> in place of <code>n - 1</code></div>
<dl><dt><span class="strong">Since:</span></dt>
  <dd>2.0</dd></dl>
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<h3>Constructor Summary</h3>
<table class="overviewSummary" border="0" cellpadding="3" cellspacing="0" summary="Constructor Summary table, listing constructors, and an explanation">
<caption><span>Constructors</span><span class="tabEnd">&nbsp;</span></caption>
<tr>
<th class="colOne" scope="col">Constructor and Description</th>
</tr>
<tr class="altColor">
<td class="colOne"><code><strong><a href="../../../../../../org/apache/commons/math3/stat/correlation/Covariance.html#Covariance()">Covariance</a></strong>()</code>
<div class="block">Create a Covariance with no data</div>
</td>
</tr>
<tr class="rowColor">
<td class="colOne"><code><strong><a href="../../../../../../org/apache/commons/math3/stat/correlation/Covariance.html#Covariance(double[][])">Covariance</a></strong>(double[][]&nbsp;data)</code>
<div class="block">Create a Covariance matrix from a rectangular array
 whose columns represent covariates.</div>
</td>
</tr>
<tr class="altColor">
<td class="colOne"><code><strong><a href="../../../../../../org/apache/commons/math3/stat/correlation/Covariance.html#Covariance(double[][],%20boolean)">Covariance</a></strong>(double[][]&nbsp;data,
          boolean&nbsp;biasCorrected)</code>
<div class="block">Create a Covariance matrix from a rectangular array
 whose columns represent covariates.</div>
</td>
</tr>
<tr class="rowColor">
<td class="colOne"><code><strong><a href="../../../../../../org/apache/commons/math3/stat/correlation/Covariance.html#Covariance(org.apache.commons.math3.linear.RealMatrix)">Covariance</a></strong>(<a href="../../../../../../org/apache/commons/math3/linear/RealMatrix.html" title="interface in org.apache.commons.math3.linear">RealMatrix</a>&nbsp;matrix)</code>
<div class="block">Create a covariance matrix from a matrix whose columns
 represent covariates.</div>
</td>
</tr>
<tr class="altColor">
<td class="colOne"><code><strong><a href="../../../../../../org/apache/commons/math3/stat/correlation/Covariance.html#Covariance(org.apache.commons.math3.linear.RealMatrix,%20boolean)">Covariance</a></strong>(<a href="../../../../../../org/apache/commons/math3/linear/RealMatrix.html" title="interface in org.apache.commons.math3.linear">RealMatrix</a>&nbsp;matrix,
          boolean&nbsp;biasCorrected)</code>
<div class="block">Create a covariance matrix from a matrix whose columns
 represent covariates.</div>
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<caption><span>Methods</span><span class="tabEnd">&nbsp;</span></caption>
<tr>
<th class="colFirst" scope="col">Modifier and Type</th>
<th class="colLast" scope="col">Method and Description</th>
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<td class="colFirst"><code>protected <a href="../../../../../../org/apache/commons/math3/linear/RealMatrix.html" title="interface in org.apache.commons.math3.linear">RealMatrix</a></code></td>
<td class="colLast"><code><strong><a href="../../../../../../org/apache/commons/math3/stat/correlation/Covariance.html#computeCovarianceMatrix(double[][])">computeCovarianceMatrix</a></strong>(double[][]&nbsp;data)</code>
<div class="block">Create a covariance matrix from a rectangular array whose columns represent
 covariates.</div>
</td>
</tr>
<tr class="rowColor">
<td class="colFirst"><code>protected <a href="../../../../../../org/apache/commons/math3/linear/RealMatrix.html" title="interface in org.apache.commons.math3.linear">RealMatrix</a></code></td>
<td class="colLast"><code><strong><a href="../../../../../../org/apache/commons/math3/stat/correlation/Covariance.html#computeCovarianceMatrix(double[][],%20boolean)">computeCovarianceMatrix</a></strong>(double[][]&nbsp;data,
                       boolean&nbsp;biasCorrected)</code>
<div class="block">Compute a covariance matrix from a rectangular array whose columns represent
 covariates.</div>
</td>
</tr>
<tr class="altColor">
<td class="colFirst"><code>protected <a href="../../../../../../org/apache/commons/math3/linear/RealMatrix.html" title="interface in org.apache.commons.math3.linear">RealMatrix</a></code></td>
<td class="colLast"><code><strong><a href="../../../../../../org/apache/commons/math3/stat/correlation/Covariance.html#computeCovarianceMatrix(org.apache.commons.math3.linear.RealMatrix)">computeCovarianceMatrix</a></strong>(<a href="../../../../../../org/apache/commons/math3/linear/RealMatrix.html" title="interface in org.apache.commons.math3.linear">RealMatrix</a>&nbsp;matrix)</code>
<div class="block">Create a covariance matrix from a matrix whose columns represent
 covariates.</div>
</td>
</tr>
<tr class="rowColor">
<td class="colFirst"><code>protected <a href="../../../../../../org/apache/commons/math3/linear/RealMatrix.html" title="interface in org.apache.commons.math3.linear">RealMatrix</a></code></td>
<td class="colLast"><code><strong><a href="../../../../../../org/apache/commons/math3/stat/correlation/Covariance.html#computeCovarianceMatrix(org.apache.commons.math3.linear.RealMatrix,%20boolean)">computeCovarianceMatrix</a></strong>(<a href="../../../../../../org/apache/commons/math3/linear/RealMatrix.html" title="interface in org.apache.commons.math3.linear">RealMatrix</a>&nbsp;matrix,
                       boolean&nbsp;biasCorrected)</code>
<div class="block">Compute a covariance matrix from a matrix whose columns represent
 covariates.</div>
</td>
</tr>
<tr class="altColor">
<td class="colFirst"><code>double</code></td>
<td class="colLast"><code><strong><a href="../../../../../../org/apache/commons/math3/stat/correlation/Covariance.html#covariance(double[],%20double[])">covariance</a></strong>(double[]&nbsp;xArray,
          double[]&nbsp;yArray)</code>
<div class="block">Computes the covariance between the two arrays, using the bias-corrected
 formula.</div>
</td>
</tr>
<tr class="rowColor">
<td class="colFirst"><code>double</code></td>
<td class="colLast"><code><strong><a href="../../../../../../org/apache/commons/math3/stat/correlation/Covariance.html#covariance(double[],%20double[],%20boolean)">covariance</a></strong>(double[]&nbsp;xArray,
          double[]&nbsp;yArray,
          boolean&nbsp;biasCorrected)</code>
<div class="block">Computes the covariance between the two arrays.</div>
</td>
</tr>
<tr class="altColor">
<td class="colFirst"><code><a href="../../../../../../org/apache/commons/math3/linear/RealMatrix.html" title="interface in org.apache.commons.math3.linear">RealMatrix</a></code></td>
<td class="colLast"><code><strong><a href="../../../../../../org/apache/commons/math3/stat/correlation/Covariance.html#getCovarianceMatrix()">getCovarianceMatrix</a></strong>()</code>
<div class="block">Returns the covariance matrix</div>
</td>
</tr>
<tr class="rowColor">
<td class="colFirst"><code>int</code></td>
<td class="colLast"><code><strong><a href="../../../../../../org/apache/commons/math3/stat/correlation/Covariance.html#getN()">getN</a></strong>()</code>
<div class="block">Returns the number of observations (length of covariate vectors)</div>
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<code><a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#clone()" title="class or interface in java.lang">clone</a>, <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#equals(java.lang.Object)" title="class or interface in java.lang">equals</a>, <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#finalize()" title="class or interface in java.lang">finalize</a>, <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#getClass()" title="class or interface in java.lang">getClass</a>, <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#hashCode()" title="class or interface in java.lang">hashCode</a>, <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#notify()" title="class or interface in java.lang">notify</a>, <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#notifyAll()" title="class or interface in java.lang">notifyAll</a>, <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#toString()" title="class or interface in java.lang">toString</a>, <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#wait()" title="class or interface in java.lang">wait</a>, <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#wait(long)" title="class or interface in java.lang">wait</a>, <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#wait(long,%20int)" title="class or interface in java.lang">wait</a></code></li>
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<pre>public&nbsp;Covariance()</pre>
<div class="block">Create a Covariance with no data</div>
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<pre>public&nbsp;Covariance(double[][]&nbsp;data,
          boolean&nbsp;biasCorrected)
           throws <a href="../../../../../../org/apache/commons/math3/exception/MathIllegalArgumentException.html" title="class in org.apache.commons.math3.exception">MathIllegalArgumentException</a>,
                  <a href="../../../../../../org/apache/commons/math3/exception/NotStrictlyPositiveException.html" title="class in org.apache.commons.math3.exception">NotStrictlyPositiveException</a></pre>
<div class="block">Create a Covariance matrix from a rectangular array
 whose columns represent covariates.

 <p>The <code>biasCorrected</code> parameter determines whether or not
 covariance estimates are bias-corrected.</p>

 <p>The input array must be rectangular with at least one column
 and two rows.</p></div>
<dl><dt><span class="strong">Parameters:</span></dt><dd><code>data</code> - rectangular array with columns representing covariates</dd><dd><code>biasCorrected</code> - true means covariances are bias-corrected</dd>
<dt><span class="strong">Throws:</span></dt>
<dd><code><a href="../../../../../../org/apache/commons/math3/exception/MathIllegalArgumentException.html" title="class in org.apache.commons.math3.exception">MathIllegalArgumentException</a></code> - if the input data array is not
 rectangular with at least two rows and one column.</dd>
<dd><code><a href="../../../../../../org/apache/commons/math3/exception/NotStrictlyPositiveException.html" title="class in org.apache.commons.math3.exception">NotStrictlyPositiveException</a></code> - if the input data array is not
 rectangular with at least one row and one column.</dd></dl>
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<pre>public&nbsp;Covariance(double[][]&nbsp;data)
           throws <a href="../../../../../../org/apache/commons/math3/exception/MathIllegalArgumentException.html" title="class in org.apache.commons.math3.exception">MathIllegalArgumentException</a>,
                  <a href="../../../../../../org/apache/commons/math3/exception/NotStrictlyPositiveException.html" title="class in org.apache.commons.math3.exception">NotStrictlyPositiveException</a></pre>
<div class="block">Create a Covariance matrix from a rectangular array
 whose columns represent covariates.

 <p>The input array must be rectangular with at least one column
 and two rows</p></div>
<dl><dt><span class="strong">Parameters:</span></dt><dd><code>data</code> - rectangular array with columns representing covariates</dd>
<dt><span class="strong">Throws:</span></dt>
<dd><code><a href="../../../../../../org/apache/commons/math3/exception/MathIllegalArgumentException.html" title="class in org.apache.commons.math3.exception">MathIllegalArgumentException</a></code> - if the input data array is not
 rectangular with at least two rows and one column.</dd>
<dd><code><a href="../../../../../../org/apache/commons/math3/exception/NotStrictlyPositiveException.html" title="class in org.apache.commons.math3.exception">NotStrictlyPositiveException</a></code> - if the input data array is not
 rectangular with at least one row and one column.</dd></dl>
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<pre>public&nbsp;Covariance(<a href="../../../../../../org/apache/commons/math3/linear/RealMatrix.html" title="interface in org.apache.commons.math3.linear">RealMatrix</a>&nbsp;matrix,
          boolean&nbsp;biasCorrected)
           throws <a href="../../../../../../org/apache/commons/math3/exception/MathIllegalArgumentException.html" title="class in org.apache.commons.math3.exception">MathIllegalArgumentException</a></pre>
<div class="block">Create a covariance matrix from a matrix whose columns
 represent covariates.

 <p>The <code>biasCorrected</code> parameter determines whether or not
 covariance estimates are bias-corrected.</p>

 <p>The matrix must have at least one column and two rows</p></div>
<dl><dt><span class="strong">Parameters:</span></dt><dd><code>matrix</code> - matrix with columns representing covariates</dd><dd><code>biasCorrected</code> - true means covariances are bias-corrected</dd>
<dt><span class="strong">Throws:</span></dt>
<dd><code><a href="../../../../../../org/apache/commons/math3/exception/MathIllegalArgumentException.html" title="class in org.apache.commons.math3.exception">MathIllegalArgumentException</a></code> - if the input matrix does not have
 at least two rows and one column</dd></dl>
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<h4>Covariance</h4>
<pre>public&nbsp;Covariance(<a href="../../../../../../org/apache/commons/math3/linear/RealMatrix.html" title="interface in org.apache.commons.math3.linear">RealMatrix</a>&nbsp;matrix)
           throws <a href="../../../../../../org/apache/commons/math3/exception/MathIllegalArgumentException.html" title="class in org.apache.commons.math3.exception">MathIllegalArgumentException</a></pre>
<div class="block">Create a covariance matrix from a matrix whose columns
 represent covariates.

 <p>The matrix must have at least one column and two rows</p></div>
<dl><dt><span class="strong">Parameters:</span></dt><dd><code>matrix</code> - matrix with columns representing covariates</dd>
<dt><span class="strong">Throws:</span></dt>
<dd><code><a href="../../../../../../org/apache/commons/math3/exception/MathIllegalArgumentException.html" title="class in org.apache.commons.math3.exception">MathIllegalArgumentException</a></code> - if the input matrix does not have
 at least two rows and one column</dd></dl>
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<pre>public&nbsp;<a href="../../../../../../org/apache/commons/math3/linear/RealMatrix.html" title="interface in org.apache.commons.math3.linear">RealMatrix</a>&nbsp;getCovarianceMatrix()</pre>
<div class="block">Returns the covariance matrix</div>
<dl><dt><span class="strong">Returns:</span></dt><dd>covariance matrix</dd></dl>
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<pre>public&nbsp;int&nbsp;getN()</pre>
<div class="block">Returns the number of observations (length of covariate vectors)</div>
<dl><dt><span class="strong">Returns:</span></dt><dd>number of observations</dd></dl>
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<h4>computeCovarianceMatrix</h4>
<pre>protected&nbsp;<a href="../../../../../../org/apache/commons/math3/linear/RealMatrix.html" title="interface in org.apache.commons.math3.linear">RealMatrix</a>&nbsp;computeCovarianceMatrix(<a href="../../../../../../org/apache/commons/math3/linear/RealMatrix.html" title="interface in org.apache.commons.math3.linear">RealMatrix</a>&nbsp;matrix,
                                 boolean&nbsp;biasCorrected)
                                      throws <a href="../../../../../../org/apache/commons/math3/exception/MathIllegalArgumentException.html" title="class in org.apache.commons.math3.exception">MathIllegalArgumentException</a></pre>
<div class="block">Compute a covariance matrix from a matrix whose columns represent
 covariates.</div>
<dl><dt><span class="strong">Parameters:</span></dt><dd><code>matrix</code> - input matrix (must have at least one column and two rows)</dd><dd><code>biasCorrected</code> - determines whether or not covariance estimates are bias-corrected</dd>
<dt><span class="strong">Returns:</span></dt><dd>covariance matrix</dd>
<dt><span class="strong">Throws:</span></dt>
<dd><code><a href="../../../../../../org/apache/commons/math3/exception/MathIllegalArgumentException.html" title="class in org.apache.commons.math3.exception">MathIllegalArgumentException</a></code> - if the matrix does not contain sufficient data</dd></dl>
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<pre>protected&nbsp;<a href="../../../../../../org/apache/commons/math3/linear/RealMatrix.html" title="interface in org.apache.commons.math3.linear">RealMatrix</a>&nbsp;computeCovarianceMatrix(<a href="../../../../../../org/apache/commons/math3/linear/RealMatrix.html" title="interface in org.apache.commons.math3.linear">RealMatrix</a>&nbsp;matrix)
                                      throws <a href="../../../../../../org/apache/commons/math3/exception/MathIllegalArgumentException.html" title="class in org.apache.commons.math3.exception">MathIllegalArgumentException</a></pre>
<div class="block">Create a covariance matrix from a matrix whose columns represent
 covariates. Covariances are computed using the bias-corrected formula.</div>
<dl><dt><span class="strong">Parameters:</span></dt><dd><code>matrix</code> - input matrix (must have at least one column and two rows)</dd>
<dt><span class="strong">Returns:</span></dt><dd>covariance matrix</dd>
<dt><span class="strong">Throws:</span></dt>
<dd><code><a href="../../../../../../org/apache/commons/math3/exception/MathIllegalArgumentException.html" title="class in org.apache.commons.math3.exception">MathIllegalArgumentException</a></code> - if matrix does not contain sufficient data</dd><dt><span class="strong">See Also:</span></dt><dd><a href="../../../../../../org/apache/commons/math3/stat/correlation/Covariance.html#Covariance(org.apache.commons.math3.linear.RealMatrix)"><code>Covariance(org.apache.commons.math3.linear.RealMatrix)</code></a></dd></dl>
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<pre>protected&nbsp;<a href="../../../../../../org/apache/commons/math3/linear/RealMatrix.html" title="interface in org.apache.commons.math3.linear">RealMatrix</a>&nbsp;computeCovarianceMatrix(double[][]&nbsp;data,
                                 boolean&nbsp;biasCorrected)
                                      throws <a href="../../../../../../org/apache/commons/math3/exception/MathIllegalArgumentException.html" title="class in org.apache.commons.math3.exception">MathIllegalArgumentException</a>,
                                             <a href="../../../../../../org/apache/commons/math3/exception/NotStrictlyPositiveException.html" title="class in org.apache.commons.math3.exception">NotStrictlyPositiveException</a></pre>
<div class="block">Compute a covariance matrix from a rectangular array whose columns represent
 covariates.</div>
<dl><dt><span class="strong">Parameters:</span></dt><dd><code>data</code> - input array (must have at least one column and two rows)</dd><dd><code>biasCorrected</code> - determines whether or not covariance estimates are bias-corrected</dd>
<dt><span class="strong">Returns:</span></dt><dd>covariance matrix</dd>
<dt><span class="strong">Throws:</span></dt>
<dd><code><a href="../../../../../../org/apache/commons/math3/exception/MathIllegalArgumentException.html" title="class in org.apache.commons.math3.exception">MathIllegalArgumentException</a></code> - if the data array does not contain sufficient
 data</dd>
<dd><code><a href="../../../../../../org/apache/commons/math3/exception/NotStrictlyPositiveException.html" title="class in org.apache.commons.math3.exception">NotStrictlyPositiveException</a></code> - if the input data array is not
 rectangular with at least one row and one column.</dd></dl>
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<h4>computeCovarianceMatrix</h4>
<pre>protected&nbsp;<a href="../../../../../../org/apache/commons/math3/linear/RealMatrix.html" title="interface in org.apache.commons.math3.linear">RealMatrix</a>&nbsp;computeCovarianceMatrix(double[][]&nbsp;data)
                                      throws <a href="../../../../../../org/apache/commons/math3/exception/MathIllegalArgumentException.html" title="class in org.apache.commons.math3.exception">MathIllegalArgumentException</a>,
                                             <a href="../../../../../../org/apache/commons/math3/exception/NotStrictlyPositiveException.html" title="class in org.apache.commons.math3.exception">NotStrictlyPositiveException</a></pre>
<div class="block">Create a covariance matrix from a rectangular array whose columns represent
 covariates. Covariances are computed using the bias-corrected formula.</div>
<dl><dt><span class="strong">Parameters:</span></dt><dd><code>data</code> - input array (must have at least one column and two rows)</dd>
<dt><span class="strong">Returns:</span></dt><dd>covariance matrix</dd>
<dt><span class="strong">Throws:</span></dt>
<dd><code><a href="../../../../../../org/apache/commons/math3/exception/MathIllegalArgumentException.html" title="class in org.apache.commons.math3.exception">MathIllegalArgumentException</a></code> - if the data array does not contain sufficient data</dd>
<dd><code><a href="../../../../../../org/apache/commons/math3/exception/NotStrictlyPositiveException.html" title="class in org.apache.commons.math3.exception">NotStrictlyPositiveException</a></code> - if the input data array is not
 rectangular with at least one row and one column.</dd><dt><span class="strong">See Also:</span></dt><dd><a href="../../../../../../org/apache/commons/math3/stat/correlation/Covariance.html#Covariance(org.apache.commons.math3.linear.RealMatrix)"><code>Covariance(org.apache.commons.math3.linear.RealMatrix)</code></a></dd></dl>
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<h4>covariance</h4>
<pre>public&nbsp;double&nbsp;covariance(double[]&nbsp;xArray,
                double[]&nbsp;yArray,
                boolean&nbsp;biasCorrected)
                  throws <a href="../../../../../../org/apache/commons/math3/exception/MathIllegalArgumentException.html" title="class in org.apache.commons.math3.exception">MathIllegalArgumentException</a></pre>
<div class="block">Computes the covariance between the two arrays.

 <p>Array lengths must match and the common length must be at least 2.</p></div>
<dl><dt><span class="strong">Parameters:</span></dt><dd><code>xArray</code> - first data array</dd><dd><code>yArray</code> - second data array</dd><dd><code>biasCorrected</code> - if true, returned value will be bias-corrected</dd>
<dt><span class="strong">Returns:</span></dt><dd>returns the covariance for the two arrays</dd>
<dt><span class="strong">Throws:</span></dt>
<dd><code><a href="../../../../../../org/apache/commons/math3/exception/MathIllegalArgumentException.html" title="class in org.apache.commons.math3.exception">MathIllegalArgumentException</a></code> - if the arrays lengths do not match or
 there is insufficient data</dd></dl>
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<pre>public&nbsp;double&nbsp;covariance(double[]&nbsp;xArray,
                double[]&nbsp;yArray)
                  throws <a href="../../../../../../org/apache/commons/math3/exception/MathIllegalArgumentException.html" title="class in org.apache.commons.math3.exception">MathIllegalArgumentException</a></pre>
<div class="block">Computes the covariance between the two arrays, using the bias-corrected
 formula.

 <p>Array lengths must match and the common length must be at least 2.</p></div>
<dl><dt><span class="strong">Parameters:</span></dt><dd><code>xArray</code> - first data array</dd><dd><code>yArray</code> - second data array</dd>
<dt><span class="strong">Returns:</span></dt><dd>returns the covariance for the two arrays</dd>
<dt><span class="strong">Throws:</span></dt>
<dd><code><a href="../../../../../../org/apache/commons/math3/exception/MathIllegalArgumentException.html" title="class in org.apache.commons.math3.exception">MathIllegalArgumentException</a></code> - if the arrays lengths do not match or
 there is insufficient data</dd></dl>
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